
Answer:
 x + 2.6 = 10.4
 x = 7.8
Step-by-step explanation:
If 2.6 liters are added to x liters with the result that 10.4 liters then exist, the model is ...
 2.6 +x = 10.4 . . . . . . . 2.6 added to x gives 10.4
The commutative property of addition lets you rewrite this to ...
 x +2.6 = 10.4
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Subtracting 2.6 from both sides of the equation gives its solution:
 x +2.6 -2.6 = 10.4 -2.6
 x = 7.8